Rod-less cylinders require a braking device as stopping means. Such a braking device generally requires additional measures to enlarge the outside dimensions of a standard cylinder. However, such a manner of construction, which leads to large outside dimensions, is undesirable for many applications.
An example of a rod-less cylinder is shown in German patent publication C2 32 29 305. In that device the power pick-up surrounds a cylinder housing and has a braking device within the inside thereof. The braking device consists of a pressure body with an angular brake lining which can be brought against a special brake path so that, upon actuating a pressure chamber which is disposed above the brake lining or the pressure body, the pressure body is pressed against the braking surface. At the same time, a support path is created on each one of the polygonal cross sections of the cylinder, and on which paths the power pick-up rests via rollers. Since the power pick-up always moves in conjunction with the piston, the feed line for the pressure fluid must also be constructed movable.
It is thus an object of the present invention to avoid the necessity of a special brake rail together with the respective brake lining and pressure body in addition to the carriage guide, but nevertheless provide an effective brake which, if at all, increases the dimensions of the unit only slightly, and, in addition, can be economically manufactured.
This and other objects are achieved in accordance with the present invention by providing a rod-less cylinder unit having a pull belt which is fastened to the end parts of the piston and is sealed off at each end of the cylinder. The piston-cylinder unit has guide pulleys for the pull-belt which are rotatably mounted on head pieces, a power pick-up fastened to the ends of the pull-belt which is movable parallel to the piston and a braking device for the piston which breaking device can be actuated by a pressure fluid. The braking device is associated with at least one of the pulleys, it is arranged within the head piece and is preferably adapted to the outer shape of the pulley and/or of the pull belt which is supported by the pulley. A feed line for the pressure fluid is connected to the stationary head piece of the unit. In this way one avoids having to arrange special brake rails over the length of the unit, which leads to a considerable increase of the structural height of the unit. It is further advantageous that the pressure fluid is no longer fed to the moving power pick-up but instead to the stationary head piece. Furthermore, the unit can be manufactured at considerably less expense.
The present invention can be constructed in accordance with the above-described basic concept by providing on the corresponding head piece of at least one pulley an intermediate piece on which a braking element is mounted facing the deflected section of the pull belt. The braking device or brake element is controllably actuated by the pressure fluid passing through a feed line in the head piece and through a channel in the wall of the brake element. This embodiment does not require more space than that required by the structural width of the unit determined by the pulley, and it utilizes the available unused space within the inside of the head piece. Preferably, the intermediate piece is rigidly attached to the head piece.
Another embodiment of the present invention provides that the brake element consists of a support section or profile which corresponds in shape to the circumferential path and the cross section of the pull belt. The brake element is surrounded by a tubular body which is closed at its ends. This results in an extremely efficient utilization of the available space and provides the largest possible braking surface.
The present invention further provides a channel for the pressure fluid disposed on the support section or support profile opposite the flexible pull belt. The pressure fluid channel which is open toward the tubular body extends transverse to the axis of rotation of the pulley and preferably, at least in part, around the deflected section of the pull belt. This substantial wrapping of the circumferential outer surface of the pulley leads to the desired largest possible braking surface.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims.